Field of the Invention and Related Art Statement
The present invention relates to an apparatus for detecting one or more unused sectors on a record medium, and more particularly to an apparatus for detecting unused sectors on a record medium such as optical disk and opto-magnetic disk which is detachably installed in a recording apparatus. In this specification, the term of "unused sector" means not only a sector in which data has not been recorded, but also a sector in which previously recorded data has been erased.
In a recording apparatus in which a record medium such as a hard disk is fixedly provided, data recorded in the hard disk is generally managed by an operating system (OS), and unused sectors in which no data has been recorded ca be found without reading respective sectors on the record medium. However, in a recording apparatus using a record medium such as optical disk and opto-magnetic disk, the record medium is not fixedly installed in the recording apparatus, but is detachably set in the recording apparatus. In such a recording apparatus, since a directory for managing the sectors is not stored in the recording apparatus, it is necessary to record a directory. To this end it is necessary to detect whether respective sectors have been used or not. Further in some operating systems (OS), the data management is effected such that the condition of record of sectors are successively checked to find a first unused sector, and then sectors following this unused sector are identified as unused sectors.
In the recording apparatus in which the optical disk or opto-magnetic disk is used as the detachable record medium, a sector is read or scanned to generate an address mark found (AMF) signal, and when the AMF signal corresponding to a synchronizing signal (SB) in a data area of the sector, it is judged that the relevant sector has been used and data has been recorded in the sector, so that new data should not be recorded in this sector.
FIG. 1A shows an example of a format of a sector in an optical disk or opto-magnetic disk, and FIGS. 1B to 1E are signal waveforms for explaining the manner of detecting the address mark found (AMF) signal. This sector format has been discussed by ISO for 5.25" WORM (Write Once Read Many type disk) and is generally adopted in the continuous servo tracking system in which the tracking error is detected by the push-pull method. As shown in FIG. 1A the sector includes, between a preformatted identification (ID area) area and a data area in which data has been recorded or is to be recorded, a mirror portion of 1 byte (1B) for detecting an offset of a tracking error signal (Offset Detection Flag: ODF), a gap of 3B (Gap), a flag of 5B (Flag), a gap of 3B (Gap), and a blank of 2B for use in controlling the laser power (Auto Laser Power Control: ALPC).
The ID area is divided into three ID portions and a postamble of 1B (PA). The first ID portion includes sector mark of 5B (SM) for indicating the head of the ID area, PLL synchronization pattern of 12B (VFO.sub.1), address mark of 1B (AM.sub.1) for indicating a start position of reading the address code data and track number, sector number and error correcting code of 5B (ID.sub.1 +CRC). The second ID portion is consisting of VFO.sub.2 of 8B, AM.sub.2 of 1B and ID.sub.2 +CRC of 5B, and similarly the third ID portion includes VFO.sub.3 of 8B, AM.sub.3 of 1B and ID.sub.3 +CRC of 5B. In order to reduce the error three address marks each having the same bit construction are recorded in the ID area. When any one of ID.sub.1, ID.sub.2 and ID.sub.3 is detected, it is judged that ID is identified.
In the data area, there is recorded PLL synchronization pattern VFO.sub.3 (which is same as VFO.sub.1) of 12B at a start position, and then synchronizing signal SB of 3B is recorded. Further a plurality of data blocks each having a length of 15 B or 20 B are recorded. In each of data blocks following the first data block, there is recorded a re-synchronizing signal of 1B (RS) at a head position. At an end portion of the data area there is further recorded a buffer portion (Buffer) of 15B for a margin for a possible variation of the rotating speed of the record disk.
When the data is read out of the record disk having the sector format shown in FIG. 1A, AMF (shown in FIG. 1B) is first obtained by detecting AM, SB and RS, and then non return zero (NRZ) and synchronized reference clock (RRCK) are derived on the basis of the detected AFM. Then these detected AMF, RRCK and NRZ are supplied to a controller for controlling a drive. FIG. 1C represents a read gate (RG) for reading the data recorded in the data area, FIG. 1D the NRZ and FIG. 1E denotes the RRCK. The reading operation is controlled by the controller in accordance with the detected AMF and reference clock (RRCK).
Therefore, in the optical disk or opto-magnetic disk having the sector format illustrated in FIG. 1A, it is possible to judge whether a sector has been used or not used by monitoring AMFs and detecting whether or not there is AMF corresponding to SB in the data area. That is to say, when the read out AMFs include AM corresponding to SB in the data area, it is judged that the relevant sector has been used, so that new data should not be written.
In a data recording and reproducing apparatus utilizing the optical disk or opto-magnetic disk having the sector format shown in FIG. 1A, AM is generated when a signal of 1B is detected among SB of 3B in order to attain a redundancy in the detecting faculty. Therefore, in some cases SB might not be detected due to the secular variation and defects on the disk. Further when the recording and reproducing operation could not be performed correctly due to error in the focus servo control and tracking servo control which might be caused by the secular variation of the optical system, SB might not be detected.
AS explained above when the unused sectors are detected by judging whether AMF corresponding to SB in the data area is existent or not, a used sector might be erroneously detected as an unused sector and new data might be written over the previously recorded data. Then the previously recorded data might be destroyed. Of course the new data could not be recorded accurately.
In order to avoid the above mentioned drawback, there have been proposed various methods for detecting the unused sectors much more correctly. Since the position of the synchronizing signal SB in the sector is fixed determined, a counter is actuated by detecting SM or AM in the ID area to count clock pulses. When SB is not detected at the predetermined timing, a signal which is generated on the basis of a predetermined count value of the counter is used as an interpolated AMF signal for SB.
FIG. 2 is a block diagram illustrating a known circuit for deriving the interpolated AMF in the manner explained above. The read signal obtained by scanning the record disk is first converted into a bivalent signal by a bivalent circuit 1, and then the thus converted bivalent signal is supplied to an SB detection circuit 2 and an SM and AM detection circuit 3. The SB detection circuit 2 detects SB in the read signal to derive an SB detection signal by processing the bivalent signal from the bivalent circuit 1, and the thus detected SB detection signal is supplied to an AMF switching circuit 4. The SM and AM detection circuit 3 receives the bivalent signal and generates an SM detection signal when SM is detected in the read signal. The AM detection signal is consisting of AM.sub.1, AM.sub.2 and AM.sub.3. The SM and AM detection circuit 3 further generates a gate signal for extracting these SM and AM detection signals. FIGS. 3A to 3C show these signals detected by the SM and AM detection circuit 3.
The SM detection signal, AM detection signal and gate signal derived by the SM and AM detection circuit 3 are supplied to an SB interpolation circuit 5. At the same time, the SM detection signal is supplied to the controller as a sector mark found signal (SMF). The AM detection signal generated by the SM and AM detection circuit 3 is supplied to one input terminal of an OR circuit 6.
The SB interpolation circuit 5 comprises NOR circuit 7, counter 8 and decoder 9. To the NOR circuit 7 are supplied the SM, AM detection signals and gate signal generated by the SM and AM detection circuit 3, and to the decoder 9 are supplied the SM and AM detection signals. The counter 8 counts clock pulses while the counter is reset by an output of the NOR circuit 7. A count value of the counter 8 is supplied to the decoder 9. The decoder receives the count value of the counter 8 and the SM and AM detection signals to derive an interpolated AMF signal shown in FIG. 3D. As shown in FIG. 2, the interpolated AMF signal thus generated is supplied to an AMF switching circuit 4. That is to say, the decoder 9 generates the interpolated AMF each time the counter 8 has counted a predetermined number of clock pulses.
The AMF switching circuit 4 operates such that when the normal AMF is not detected by the SB detection circuit 2, the interpolated AMF generated by the SB interpolation circuit 5 is supplied to the other input terminal of the OR circuit 6. It should be noted that when the normal AMF is detected by the SB detection circuit 2, the normal AMF detection signal is supplied to the OR circuit 6 via the AMF switching circuit 4. In this manner even when the normal AMF is not detected for the used sector due to the various factors, the interpolated AMF signal is supplied from the OR circuit 6, so that it is effectively possible to prevent the recorded data from being destroyed
However, in the known apparatus, for unused sectors there is also produced the interpolated AMF signal, it is impossible to detect the unused sectors.
In Japanese Patent Application Laid-open Publication Kokai Sho 60-164834, there is described another known apparatus for detecting unused sectors In this known apparatus, a synchronizing data mark is recorded at a front end of a sector each time data is recorded in a sector, and when a predetermined number of sectors having no data marks are detected, it is judged that a first sector of these sectors is a front one of a series of unused sectors. However, this known apparatus has no means for removing the influence of the defects on the record medium and the secular variation of the optical system. That is to say, if the data marks of used sectors are not detected correctly due to the defects on the record medium, the used sectors might be detected as unused sectors and thus the previously recorded data is destroyed.